It doesn't sound like the current M5/M6 V10. Perhaps a different exhaust system on a V8 and higher redline?

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Took delivery of our M5 on 8/28/2006 in Munich
Black Saphire, all options except CA and window shades
Car boarded Vessel Undine on 9/14, arrived in port U.S. 9/28
Took re-delivery on 10/20/2006 (six weeks to the day)Our ED Experience